1. Field of the Invention
This invention relates to a pseudo GPS signal transmitting system in a base station which is installed on the ground and transmits a pseudo GPS signal for use as one of GPS satellites.
2. Description of the Related Art
To use a conventional base station as one of GPS satellites in determining the position, the time system of the base station is controlled according to the GPS time. Specifically, just as each GPS satellite transmits a distance-measuring signal in synchronization with the GPS time, the base station also transmits a distance-measuring signal (a pseudo GPS signal) of a specified reference point in synchronization with the GPS time.
However, since the Department of Defense has been implementing a selective availability (SA) policy, whereby the accuracy of GPS time is forced to deteriorate, it is very difficult to accurately monitor the GPS time serving as a reference in a base station.
Such monitoring errors in the GPS time in a base station affect the accuracy of measuring distance between the base station and the user's GPS receiver, consequently degrading the position-determining accuracy of the user's GPS receiver.